The relative motions of individual objects viewed as an observer moves, as in looking at trees in a forest when driving past. Thus, objects closer to you move further across your field of vision than those at a distance. It is one of the monocular cues for depth perception. Animals without binocular vision (i.e., without stereopsis or overlapping visual fields) use motion parallax in order to see depth (e.g., head bobbing by pigeons). There is a lack of research on the development of the ability to extract depth from motion parallax despite the fact it has been known for some time that young infants are sensitive to motion as well depth-from-motion cues. One study, following up infants under monocular viewing conditions from 8 to 29 weeks longitudinally and using a habituation-dishabituation paradigm, reported that infants become sensitive to unambiguous depth perception between 14 and 20 weeks of age.
See Binocular vision, Depth perception, Habituation, Kinetic depth information, Motion perception, Pictorial depth perception, Relative distance, Stereoscopic depth perception